Llywelyn ap Seisyll

Llywelyn ap Seisyll (978-1023) was King of Gwynedd from 1018 to 1023 (succeeding Aeddan ap Blegywryd and preceding Iago ab Idwal ap Meurig) and King of Deheubarth from 1018 to 1023 (succeeding Cadell ab Einion and preceding Rhydderch ap Iestyn).

Biography
Llywelyn ap Seisyll was born into a noble family, and he seized power in Gwynedd and Powys in 1018 after defeating and killing Aeddan ap Blegywryd and four of his sons. In 1022, Llywelyn's brother-in-law Rhain the Irishman claimed the throne of Deheubarth, and Llywelyn slew Rhian at Abergwili. He was therefore able to rule Deheubarth until his death in 1023.